Does anyone have a solution for plywood over a concrete wall short of flashing the entire expanse? I realize this is a rather poor application for plywood to begin with but I could use a solution. Is there a paint-on product someone finds reliable? Maybe a sheet/paper good? Bituthane? I’ve come up against this question more than once and I’d love to have a reliable way of handling it. For more on the particular situation see the long winded explanation below. It gets complicated. Feel free to stick to the more straight forward question asked above. Any help is appreciated!
-Mike Cobb
Additional information:
I’m an architect in the Northern California’s wine country. I’ve got a pool house I’m working on right now. The foundation is a slab on grade. Actually the site slopes about 4′ across the length of the buiding. What starts out as a slab on grade condition winds up being about a 4-feet-above-grade condition on the downhill side. We’ll be filling the the stem wall perimeter with gravel and pouring the slab on top of that. The owners want a rustic barn feel to the pool house. What this amounts to in their eyes is exposed studs on the inside above a 3 foot high wainscotting. At least above the wanscotting, the exterior cladding will likely be a 3/4″ AC plywood. This has been selected to give a relatively attractive interior finish while also providing enough screwing meat to attach 1×12 rough sawn vertical redwood siding to the outside of the building. An additional complication is this: There is a reverse-benderboard-batten applied behind the vertical joint that exists where two 1×12 redwood boards meet. This is to avoid the sight of building paper when the boards weather and shrink. We use this detail a lot out at Sea Ranch on the coast.
I would like the siding to continue down the 4′ face of the concrete stem wall to give this building a more finished look (I realize this may seem a contradiction of the rustic idea. Tough!).
My question is this: How would one best achieve this? With the the 3/4″ plywood substrate there is the possibility of shooting 3/4″ horizontal furring strips into the face of the concrete where there would otherwise be lywood but the bender board will not stay up against the 1×12 boards in between the furring strips. The best solution seems to be applying 3/4″ plywood right down the face of the concrete but I’m concerned about putting wood right up against concrete.
Replies
You should be able to use pressure treated plywood. Just north of you here, they make the stuff, using Doug Fir AC plywood, .40 treatment. When it's dry, it can be painted or just about anything else you want to do with it. Install it to the concrete with Tapcon screws (and adhesive, if you desire).
I use it against concrete walls in situations similar to yours, for boat house ramps, sheeting for indoor showers prior to installing membranes and tile backer, etc. Never had any problems, partly because, as I specified above, it is AC grade and has good faces.
Usually available here in 1/2" and 3/4" 4 X 8's.
email me if you can't find a source.
Edited 2/24/2003 10:13:08 PM ET by Notchman
The stuff commonly available (even in Home Depot) is 0.6 psf. Intended use is for permanent wood foundations.
Carpenter ants seem to love untreated plywood that's in contact with concrete. Needless to say, that's not a problem with this stuff.
PT Plywood
If you haven't poured the concrete yet, I would use pressure treated for the forms and leave it in place.
If you already poured, I would use PL Premium adhesive and glue it to the crete with nailing shot on powder actuated ram
If they have insane environmental objections to having PT on the property, apply a layer of ice and water shield between the crete and the 3/4" ply
I like the reverse B&B idea. It allows a breather space behind the siding boards. They ought to last just about forever. Or atleast until we die.
Here's a shot or two of an interior similat to what you describe. It was sheathed with pine shiplap boards. Started out to be one of Maine's vernacular summer camps but it got nice as we went along.
Excellence is its own reward!
I've got a pretty good picture in my head of the reverse bender board detail you describe but I've never seen it used. Sounds like a great idea.
If you use treated 3/4" horizontal furring strips could you in-fill between them with 3/4" foam insulation to back up your bender boards? If you think it would provide sufficient strength I would recommend Perform Guard EPS. It is treated with a natural mineral additive called Timbor that resists insect infestation such as carpenter ants and termites. Insects don't eat EPS foam but they do like to tunnel and nest in it.
I see from your profile that this is your first post. Welcome to Breaktime- hope you stick around and chip in when you can. I for one, welcome the benefit of your professional experience.
Kevin Halliburton
"One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man." -Elbert Hubbard-
Thanks for the advice and the kinds words Kevin.
-Mike Cobb
And I really appreciate those who provide their profiles. So far, I've personally met one (1) Breaktime member and his spouse, who turned out to be top notch people, and another sent me a really nice freeby, but it's always a benefit to put a face and a place with a name.
Welcome!
Michael, Is there anything wrong with this simple (and relatively non-toxic and economical solution)? Drape 30 pound felt behind the plywood. Attach your 3/4 ply over the felt with tapcons. At the lower edge of the ply, run a strip of 1x4 redwood, also applied with tapcons. Possibly apply adhesive or caulk behind the 3/4 strip to discourage insect penetration. I think this approach might take care of all your concerns, but I may be overlooking something.
By the way, there is nothing extreme about wanting to avoid the use of the toxic PT material. It's deadly stuff. I have not allowed it on my job sites for years. The less exposure to toxics we can manage, the better.
good luck, david gerstel
David-
Your response is simple and compelling. Thanks for putting it down. So often we look for a solution that will simply make the installation last the longest. The difference between your solution and a pressure treated one in terms of life cycle is probably minimal compared to the large difference in environmental virtues. Thanks for the two cents.
-Mike